Superconducting magnets are used in a variety of contexts, including nuclear magnetic resonance (NMR) analysis, and magnetic resonance imaging (MRI). To realize superconductivity, a magnet is maintained in a cryogenic environment at a temperature near absolute zero. Typically, the magnet includes one or more electrically conductive coils which are disposed in a cryostat and through which an electrical current circulates to create the magnetic field.
There are many ways to maintain the electrically conductive coil(s) at cryogenic temperatures so that they are superconducting during normal operation.
One method is to employ one or more cooling tubes in a cooling loop to circulate a gas between the electrically conductive coil(s) and a cold station so as to transfer heat from the electrically conductive coil(s) and the cold station. The cold station is typically some structure with a relatively large thermal mass, and can be used to keep the electrically conductive coils cold for a short period of time if the refrigeration system is turned off or is not operative. Such cooling tube(s) may efficiently transfer heat from the electrically conductive coil to the cold station whenever the cold station is at a lower temperature than the electrically conductive coil(s).
However, in some situations it is possible for conditions within the cryostat to degrade and the temperature of the magnet (i.e., electrically conductive coil(s)) may begin to rise. This may happen, for example, if refrigeration capability for the cryogenic environment is lost, for example due to a loss of electrical power for the compressor (i.e., a power outage). At a certain point, if cooling of the magnet's environment within the cryostat is not restored, then the magnet's temperature will rise to reach the so-called critical temperature where the magnetic field will “quench” and the magnet will convert its magnetic energy to heat energy. In that case, the temperature of the electrically conductive coil(s) may rise well above the cold station's temperature, and the heat sink capacity of the cold station may be wasted. Furthermore, if the cold station is heated by the electrically conductive coil(s), it may need to be re-cooled by the cryostat's refrigeration system in order to bring the superconducting magnet system back to normal operation. This can cause the time to recover from a quench to be extended.
Additionally, in some superconducting magnet systems (for example, so-called “cryofree systems”) the magnet is maintained in a vacuum environment and is cooled by a sealed system (e.g., a cold plate) which is filled with a cryogenic fluid, for example liquid helium. In such systems, it is beneficial to provide a getter on or near the cold station within the vacuum environment so as to absorb stray molecules that may be released into the vacuum, as such stray molecules can become a mechanism for heat transfer. In that case, if the cold station is allowed to heat up, then the stray molecules which have been captured by the getter may be released into the chamber. If that occurs, an expensive and time-consuming vacuum pump down of the cryostat may be required to remove the released molecules.
Therefore, in a case where an electrically conductive coil rises in temperature as the magnetic field is quenched, it would be desirable to thermally disconnect or isolate the electrically conductive coil from the cold station so that the heat from the electrically conductive coil does not heat up the cold station. More specifically, in a case where the magnetic field is quenched and the electrically conductive coil rises in temperature, it would be desirable to open the cooling loop which would otherwise transfer heat from the electrically conductive coil to the cold station.
However, because the cooling loop typically has high gas (e.g., helium gas) inside, is disposed in a high vacuum environment, and operates at very low cryogenic temperatures, manual valves or solenoid operated valves (which also have large heat dissipation) are not very suitable for controlling flow within the cooling loop, for example to prevent circulation within the cooling loop when the electrically conductive coil is heated due to a quench.
Accordingly, it would be desired to provide a method and device for automatically prevent circulation within the cooling loop when the electrically conductive coil is heated dues to a quench without external control.
One aspect of the present invention can provide a method including: actuating a valve of a convective cooling loop between a closed position and an open position via a magnetic field generated by at least one electrically conductive coil disposed within a cryostat, wherein actuation of the valve controls flow of a gas disposed within the convective cooling loop.
In some embodiments, the method can further include cooling the electrically conductive coil via a sealed system having liquid helium disposed therein.
In some embodiments, opening the valve in the convective cooling loop can include displacing a magnetically reactive sealing element of the valve with respect to a sealing surface of the valve in response to the magnetic field having at least the threshold magnetic field gradient, to thereby open the valve.
In some embodiments, actuating the valve in the convective cooling loop can include displacing a magnetically reactive element of the valve in response to the magnetic field having at least the threshold magnetic field gradient, wherein displacing the magnetically reactive element causes a nonmagnetic sealing element of the valve to be displaced with respect to a sealing surface of the valve to open the valve.
In some embodiments, actuating the valve in the convective cooling loop can include employing at least one of gravity and a force produced by a pressure of the gas to cause a sealing element of the valve to be disposed against a sealing surface of the valve to close the valve.
In some embodiments, actuating the valve in the convective cooling loop can include employing a force produced by a spring in the valve to cause a sealing element of the valve to be disposed against a sealing surface of the valve to close the valve.
In some embodiments, actuating the valve in the convective cooling loop in response to the magnetic field can include applying the magnetic field oriented in a direction perpendicular to direction of a flow of the gas from an inlet of the valve to an outlet of the valve to open the valve.
In some embodiments, actuating the valve in the convective cooling loop in response to the magnetic field can include applying the magnetic field oriented in a direction parallel to direction of a flow of the gas from an inlet of the valve to an outlet of the valve to open the valve.
Another aspect of the present invention can provide an apparatus including: a convective cooling loop; and a valve configured to control a flow of a gas disposed within the convective cooling loop, wherein the valve is configured to be actuated between an open position and a closed position via a magnetic field generated by at least one electrically conductive coil disposed within a cryostat.
In some embodiments, the valve can include a sealing element and a sealing surface configured so that when the electrically conductive coil is not energized, the sealing element is mated to the sealing surface such that the valve is closed so as to prevent the flow of the gas within the cooling loop, and a magnetically reactive element, wherein in response to the magnetic field of the electrically conductive coil, the magnetically reactive element is configured to cause the sealing element to be displaced with respect to the sealing surface such that the valve is opened and the flow of the gas within the cooling loop is enabled.
In some embodiments, the magnetically reactive element can include a ferromagnetic material.
In some embodiments, the sealing element can include the magnetically reactive element.
In some embodiments, the sealing element can be nonmagnetic, and the magnetically reactive element can be attached to the sealing element such that when the magnetically reactive element is displaced by the magnetic field of the electrically conductive coil, the magnetically reactive element can in turn displace the sealing element with respect to the sealing surface such that the valve can be opened.
In some embodiments, when the electrically conductive coil is not energized, the sealing element can be held against the sealing surface at partially by gravity to close the valve.
In some embodiments, the valve can further include a spring, wherein when the electrically conductive coil is not energized, the sealing element can be held against the sealing surface at partially by a force produced by the spring to close the valve.
In some embodiments, the valve further includes a lever having a beam and a fulcrum, wherein the magnetically reactive element can be disposed at a first end of the lever at a first side of the fulcrum, and the sealing element can be disposed at a second end of the lever at a second side of the fulcrum, wherein when the magnetically reactive element is displaced by the magnetic field of the electrically conductive coil it can operate the lever so as to displace the sealing element with respect to the sealing surface such that the valve can be opened.
Yet another aspect of the present invention can provide an apparatus including: a cooling tube configured to circulate a gas therethrough to allow thermal energy to be transferred from a first device to a second device; and a valve disposed in a gas flow path of the cooling tub. The valve can include: a valve housing having an inlet and an outlet, and a sealing element and a sealing surface disposed within the valve housing, wherein the sealing element can be configured to be displaced with respect to the sealing surface to switch the valve between an open position and a closed position via a magnetic field.
In some embodiments, the sealing element can be configured to be mated to the sealing surface to close the valve and prevent a flow of the gas between the inlet and the outlet in the absence of the magnetic field, and is further configured to be displaced with respect to the sealing surface to open the valve and permit a flow of the gas between the inlet and the outlet in the presence of the magnetic field.
In some embodiments, the seating element can include a magnetically reactive material.